python-shamir-mnemonic
Reference implementation of SLIP-0039: Shamir's Secret-Sharing for Mnemonic Codes
Abstract
This SLIP describes a standard and interoperable implementation of Shamir's secret sharing (SSS). SSS splits a secret into unique parts which can be distributed among participants, and requires a specified minimum number of parts to be supplied in order to reconstruct the original secret. Knowledge of fewer than the required number of parts does not leak information about the secret.
Specification
See https://github.com/satoshilabs/slips/blob/master/slip-0039.md for full specification.
Security
This implementation is not using any hardening techniques. Secrets are passed in the open, and calculations are most likely trivially vulnerable to side-channel attacks.
The purpose of this code is to verify correctness of other implementations. It should not be used for handling sensitive secrets.
Installation
With pip from GitHub:
$ pip3 install shamir-mnemonic
From local checkout for development:
$ python3 setup.py develop
CLI usage
CLI tool is included as a reference and UX testbed.
Warning: this tool makes no attempt to protect sensitive data! Use at your own risk. If you need this to recover your wallet seeds, make sure to do it on an air-gapped computer, preferably running a live system such as Tails.
When the shamir_mnemonic
package is installed, you can use the shamir
command:
$ shamir create 3of5 # create a 3-of-5 set of shares
$ shamir recover # interactively recombine shares to get the master secret
You can supply your own master secret as a hexadecimal string:
$ shamir create 3of5 --master-secret=cb21904441dfd01a392701ecdc25d61c
You can specify a custom scheme. For example, to create three groups, with 2-of-3, 2-of-5, and 4-of-5, and require completion of all three groups, use:
$ shamir create custom --group-threshold 3 --group 2 3 --group 2 5 --group 4 5
Use shamir --help
or shamir create --help
to see all available options.
If you want to run the CLI from a local checkout without installing, use the following command:
$ python3 -m shamir_mnemonic.cli
Test vectors
The test vectors in vectors.json are given as a list of triples. The first member of the triple is a description of the test vector, the second member is a list of mnemonics and the third member is the master secret which results from combining the mnemonics. The master secret is encoded as a string containing two hexadecimal digits for each byte. If the string is empty, then attempting to combine the given set of mnemonics should result in error. The passphrase "TREZOR" is used for all valid sets of mnemonics.